[R-390] ssb stand alone product detector
jm
josemic at gmail.com
Sun Jan 19 15:15:22 EST 2020
I have seen on ebay an external product detector without make or
manufacturer signs. It is identified as SSB-1A Product detector.
It is one of the several devices that I've found to connect to the IF
output of the r390a. Until now I have seen similar circuits that needed an
external audio amplifier to perform their function.
This one is different because the connections are marked as Diode load and
IF out. It surprises me that one of them should be an input to the r390a. I
thought (erroneusly perhaps) that both diode load and If are outputs of
the receiver.
I don't find out what the way of operating on this configuration is
This is the link
https://www.ebay.com/itm/SSB-1A-Product-Detector-for-R-390A-Receiver/283743872204?hash=item421073e4cc:g:FeEAAOSw1kpeHhZn
Someone could shed some light about?
Regards
Jose
EA8DCP
El vie., 17 ene. 2020 a las 13:45, <r-390-request at mailman.qth.net> escribió:
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> 1. Re: [MRCA] Working on the R-392 (David Olean)
> 2. Re: Working on the R-392 (David Olean)
> 3. Re: Working on the R-392 (Larry H)
> 4. Re: [MRCA] Working on the R-392 (Charles Steinmetz)
> 5. Re: Working on the R-392 (David Olean)
>
>
> ----------------------------------------------------------------------
>
> Message: 1
> Date: Thu, 16 Jan 2020 16:16:52 +0000
> From: David Olean <k1whs at metrocast.net>
> To: J Mcvey <ac2eu at yahoo.com>, R-390 Forum <r-390 at mailman.qth.net>,
> "MRCA (Military Radio List)" <mrca at mailman.qth.net>
> Subject: Re: [R-390] [MRCA] Working on the R-392
> Message-ID: <2569aa3b-c8c9-63a5-35cb-ed17fc0f9680 at metrocast.net>
> Content-Type: text/plain; charset=utf-8; format=flowed
>
> I live in Maine and heat build up is not a great problem here. The joke
> here is that our summer runs from July 1 thru July 6. I have run my
> R-392s in their case and temps seem OK.? If I lived in SC or Florida, I
> might come to a different conclusion.? I actually had a MIL 26A7 SS
> replacement that I inherited from my army days. I sold it on EBay before
> I ended up with three R-392 receivers. Two of the R-392s had small
> diodes in the 12AU7 tube.sockets. I left them there except that I fitted
> gold plated pins from a DB-25 plug to each diode lead for a 100%
> positive fit to the tube socket. Maybe I will replace the audio amp at
> some point. You are sure right that it does get warm.
>
> I saved the little 2000 pf mica cap for posterity.? It was a good
> learning experience for me. Looking at the circuit, it was in the 1st RF
> output stage. It had 28 volts DC on it, but the capacitor was floating
> and not referenced to ground. The only voltage across the capacitor was
> that developed by RF signals and the plate swing of the 1st RF tube.?
> I'll bet there are plenty more of these silver mica caps getting ready
> to quit.
>
> 73
>
> Dave K1WHS
>
>
> On 1/16/2020 2:51 PM, J Mcvey wrote:
> > The problem components always seem to hide in the most inaccessible
> > places, don't they?
> >
> > Did you solid state the 26a7 yet?
> > The R-392 runs a lot cooler without the 15 watt 26A7 heater !
> >
> > I replaced the 12au7s with 1n4148 diodes also. Works fine. only one of
> > the 12au7 sections is used as a triode and that is the IF output
> > buffer for the front panel.
> > I replaced that section with a fet.
> > It was relatively easy to solid state the detector, audio section and
> > oscillators, but the IF and RF sections are a lot more challenging, so
> > I have let them alone for now.
> >
> > On Thursday, January 16, 2020, 2:17:36 AM EST, David Olean
> > <k1whs at metrocast.net> wrote:
> >
> >
> > I finally figured out that my severe distortion was only affecting one
> > band. Any strong station in the BC band between 1 and 2 MHz was
> > distorted. It was interesting that stations between 500 and 1000 kHz
> > were fine.? I had originally thought that my AGC circuitry must be bad.
> > I traced the problem to some noise coming from the tuned coils after the
> > first RF stage. I used a dual trace scope to ferret out the noise and
> > used the R-392 RF stage test points for connecting the scope probes. The
> > correct one with noise was Z-208. I took the tuning rack apart and
> > removed the RF coil. Inside were a couple of silver mica postage stamp
> > caps and the coil. I tested each cap with a Fluke DVM. each cap showed
> > infinite resistance. I put some DC voltage across the 2000 pf postage
> > stamp and saw almost all of the DC voltage show up on the other end. It
> > was shorting out.? At first, I thought I hooked it up wrong. I couldn't
> > believe my eyes. It was leaking so badly, it was almost a complete short
> > at 50 volts. I then tried low voltage across it, and saw the cap worked
> > fine up to about 8 volts DC. Then a little DC started to leak through.
> > It was only when I ramped things up to 12 or 14 volts and then it broke
> > down and allowed almost all the DC voltage to pass through! What was
> > strange was that I could blow on the capacitor and the leaking voltage
> > would drop to almost zero! This was shorting out when strong BC stations
> > were going through the RF stage. No wonder I was having problems.? I
> > only found it due to the static noise it was making occasionally as it
> > was sitting there in the circuit.
> >
> > So all the Sprague Vitamin-Q caps were fine, and it was a silver mica
> > postage stamp type capacitor? inside an RF transformer that was giving
> > me grief!
> >
> >
> > 73
> >
> > Dave K1WHS
> >
> > ______________________________________________________________
> > MRCA mailing list
> > Home: http://mailman.qth.net/mailman/listinfo/mrca
> > Help: http://mailman.qth.net/mmfaq.htm
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>
> ------------------------------
>
> Message: 2
> Date: Thu, 16 Jan 2020 16:31:40 +0000
> From: David Olean <k1whs at metrocast.net>
> To: Charles Steinmetz <csteinmetz at yandex.com>, r-390 at mailman.qth.net
> Subject: Re: [R-390] Working on the R-392
> Message-ID: <1ede737e-d223-acd5-ab08-343960c3f25f at metrocast.net>
> Content-Type: text/plain; charset=utf-8; format=flowed
>
> Thanks for the comments, Charles,
>
> Yes, I think I will be replacing many of those postage stamp types as
> time goes on.? I like the term "hoe".?? Many of the rigs I have been
> restoring were obtained from Land Air Communications. I am not sure if
> the previous work that I have seen on this gear was done there or the
> units were like that when Land Air received them.? All I know is that
> the work was shoddy and I spent much time undoing damage caused by
> previous repairs. Garden tools sounds about right.? Another term that I
> recall was from Glen, K1GW who described his repair acumen as akin to
> using blow torch and boxing gloves.
>
> 73
>
> Dave K1WHS
>
> On 1/16/2020 8:06 AM, Charles Steinmetz wrote:
> > David wrote:
> >
> >> So all the Sprague Vitamin-Q caps were fine, and it was a silver mica
> >> postage stamp type capacitor? inside an RF transformer that was giving
> >> me grief!
> >
> > In the ~60 years I've been playing with radios and other electronic
> > gear, I can only recall finding one bad Vitamin-Q -- and there is a
> > very good chance that one was damaged by the hoe who tried to fix the
> > radio before me.? [For those who haven't heard the term before, "hoe"
> > refers to someone who leaves electronic equipment looking like it was
> > worked on with garden tools.]
> >
> > By contrast, postage-stamp micas are dying like flies now.? The time
> > is nearing -- if it isn't here already -- when they should be replaced
> > shotgun-style, like plastic-cased paper caps.
> >
> > Epoxy-dipped silver micas have generally been very reliable unless
> > they had spent time underwater, but old ones have started to show EOL
> > failures over the last 20 years or so.? I expect this trend to
> > accelerate as they age further.
> >
> > Best regards,
> >
> > Charles
> >
> >
> > ______________________________________________________________
> > R-390 mailing list
> > Home: http://mailman.qth.net/mailman/listinfo/r-390
> > Help: http://mailman.qth.net/mmfaq.htm
> > Post: mailto:R-390 at mailman.qth.net
> >
> > This list hosted by: http://www.qsl.net
> > Please help support this email list: http://www.qsl.net/donate.html
>
>
> ------------------------------
>
> Message: 3
> Date: Thu, 16 Jan 2020 18:03:55 -0800
> From: Larry H <larry41gm at gmail.com>
> To: David Olean <k1whs at metrocast.net>
> Cc: R-390 Forum <r-390 at mailman.qth.net>
> Subject: Re: [R-390] Working on the R-392
> Message-ID:
> <
> CAOSJ_nuG9xYXiJn80+J8joNmUaWiT4SWnhDbBpKNsR3kjyKb7Q at mail.gmail.com>
> Content-Type: text/plain; charset="UTF-8"
>
> Dave, Nice work. Thanks for letting us know what and how you found it.
> It's good to hear the blow by blow story. Sadly, I have been relegated to
> fix the noisy bath exhaust fan. I'd rather by R-390(x)ing.
>
> As Charles said, we are seeing more and more silver micas bite the dust.
>
> Regards, Larry
>
>
> On Wed, Jan 15, 2020 at 11:17 PM David Olean <k1whs at metrocast.net> wrote:
>
> > I finally figured out that my severe distortion was only affecting one
> > band. Any strong station in the BC band between 1 and 2 MHz was
> > distorted. It was interesting that stations between 500 and 1000 kHz
> > were fine. I had originally thought that my AGC circuitry must be bad.
> > I traced the problem to some noise coming from the tuned coils after the
> > first RF stage. I used a dual trace scope to ferret out the noise and
> > used the R-392 RF stage test points for connecting the scope probes. The
> > correct one with noise was Z-208. I took the tuning rack apart and
> > removed the RF coil. Inside were a couple of silver mica postage stamp
> > caps and the coil. I tested each cap with a Fluke DVM. each cap showed
> > infinite resistance. I put some DC voltage across the 2000 pf postage
> > stamp and saw almost all of the DC voltage show up on the other end. It
> > was shorting out. At first, I thought I hooked it up wrong. I couldn't
> > believe my eyes. It was leaking so badly, it was almost a complete short
> > at 50 volts. I then tried low voltage across it, and saw the cap worked
> > fine up to about 8 volts DC. Then a little DC started to leak through.
> > It was only when I ramped things up to 12 or 14 volts and then it broke
> > down and allowed almost all the DC voltage to pass through! What was
> > strange was that I could blow on the capacitor and the leaking voltage
> > would drop to almost zero! This was shorting out when strong BC stations
> > were going through the RF stage. No wonder I was having problems. I
> > only found it due to the static noise it was making occasionally as it
> > was sitting there in the circuit.
> >
> > So all the Sprague Vitamin-Q caps were fine, and it was a silver mica
> > postage stamp type capacitor inside an RF transformer that was giving
> > me grief!
> >
> >
> > 73
> >
> > Dave K1WHS
> >
> > ______________________________________________________________
> > R-390 mailing list
> > Home: http://mailman.qth.net/mailman/listinfo/r-390
> > Help: http://mailman.qth.net/mmfaq.htm
> > Post: mailto:R-390 at mailman.qth.net
> >
> > This list hosted by: http://www.qsl.net
> > Please help support this email list: http://www.qsl.net/donate.html
>
>
> ------------------------------
>
> Message: 4
> Date: Fri, 17 Jan 2020 02:16:05 -0500
> From: Charles Steinmetz <csteinmetz at yandex.com>
> To: r-390 at mailman.qth.net
> Subject: Re: [R-390] [MRCA] Working on the R-392
> Message-ID: <5E215F35.3010603 at yandex.com>
> Content-Type: text/plain; charset=utf-8; format=flowed
>
> David wrote:
>
> > Maybe I will replace the audio amp at some point.
> > You are sure right that it does get warm.
>
> Getting rid of the heat is certainly a good idea, but an even better
> reason to do something about the 26A7 output amplifier is that it
> improves the audio quality by about a million percent.
>
> There is a very simple modification that works extremely well, my "super
> simple audio mod." Documentation is posted at
> <http://www.ko4bb.com/getsimple/index.php?id=manuals> [file name "R392
> 26A7 super simple audio mod.pdf"]. Whether you want to do this mod or
> not, it may be worth a read -- this file explains what is wrong with the
> existing 26A7 amplifier and why it sounds so very, very bad.
>
> The best fix, IMO, is to replace the 26A7 with two power MOSFETs as
> drawn by someone named "S. Johnson" in 1991. That schematic, with my
> annotations, can be downloaded from
> <http://www.ko4bb.com/getsimple/index.php?id=manuals> by searching for
> the file named "R392 26A7 MOSFET replacement Johnson annotated
> updated.pdf." [NOTE: there is an older file posted there that does NOT
> have "updated" in the file name. You want the updated file.]
>
> An annotated schematic of the stock audio amplifier is posted there as
> well, for reference [file name "392 audio amp schematic V606 607 608
> annotated.pdf"].
>
> Best regards,
>
> Charles
>
>
>
>
> ------------------------------
>
> Message: 5
> Date: Fri, 17 Jan 2020 13:45:07 +0000
> From: David Olean <k1whs at metrocast.net>
> To: Larry H <larry41gm at gmail.com>
> Cc: R-390 Forum <r-390 at mailman.qth.net>
> Subject: Re: [R-390] Working on the R-392
> Message-ID: <ee6eb8d6-dde2-a450-8857-79ce72f64007 at metrocast.net>
> Content-Type: text/plain; charset=utf-8; format=flowed
>
> Hi Larry
>
> Well, the project isn't quite over.? I have noticed that the AGC sags as
> the set warms up. A -25 dBm BC signal will drive the AGC up to about
> -2.7 volts, but after an hour or so, it only rises to about 1.7 volts. I
> checked two receivers, and both are doing the same thing.? It must be a
> leaky cap. I need to buy some freeze mist to find it. If the AGC sags, I
> start to hear a bit of distortion on strong signals.
>
> Dave K1WHS
>
> On 1/17/2020 2:03 AM, Larry H wrote:
> > Dave, Nice work.? Thanks for letting us know what and how you found
> > it.? It's good to hear the blow by blow story. Sadly, I have been
> > relegated to fix the noisy bath exhaust fan.? I'd rather by R-390(x)ing.
> >
> > As Charles said, we are seeing more and more silver micas bite the dust.
> >
> > Regards, Larry
> >
> >
> > On Wed, Jan 15, 2020 at 11:17 PM David Olean <k1whs at metrocast.net
> > <mailto:k1whs at metrocast.net>> wrote:
> >
> > I finally figured out that my severe distortion was only affecting
> > one
> > band. Any strong station in the BC band between 1 and 2 MHz was
> > distorted. It was interesting that stations between 500 and 1000 kHz
> > were fine.? I had originally thought that my AGC circuitry must be
> > bad.
> > I traced the problem to some noise coming from the tuned coils
> > after the
> > first RF stage. I used a dual trace scope to ferret out the noise and
> > used the R-392 RF stage test points for connecting the scope
> > probes. The
> > correct one with noise was Z-208. I took the tuning rack apart and
> > removed the RF coil. Inside were a couple of silver mica postage
> > stamp
> > caps and the coil. I tested each cap with a Fluke DVM. each cap
> > showed
> > infinite resistance. I put some DC voltage across the 2000 pf postage
> > stamp and saw almost all of the DC voltage show up on the other
> > end. It
> > was shorting out.? At first, I thought I hooked it up wrong. I
> > couldn't
> > believe my eyes. It was leaking so badly, it was almost a complete
> > short
> > at 50 volts. I then tried low voltage across it, and saw the cap
> > worked
> > fine up to about 8 volts DC. Then a little DC started to leak
> > through.
> > It was only when I ramped things up to 12 or 14 volts and then it
> > broke
> > down and allowed almost all the DC voltage to pass through! What was
> > strange was that I could blow on the capacitor and the leaking
> > voltage
> > would drop to almost zero! This was shorting out when strong BC
> > stations
> > were going through the RF stage. No wonder I was having problems.? I
> > only found it due to the static noise it was making occasionally
> > as it
> > was sitting there in the circuit.
> >
> > So all the Sprague Vitamin-Q caps were fine, and it was a silver mica
> > postage stamp type capacitor? inside an RF transformer that was
> > giving
> > me grief!
> >
> >
> > 73
> >
> > Dave K1WHS
> >
> > ______________________________________________________________
> > R-390 mailing list
> > Home: http://mailman.qth.net/mailman/listinfo/r-390
> > Help: http://mailman.qth.net/mmfaq.htm
> > Post: mailto:R-390 at mailman.qth.net <mailto:R-390 at mailman.qth.net>
> >
> > This list hosted by: http://www.qsl.net
> > Please help support this email list: http://www.qsl.net/donate.html
> >
>
>
> ------------------------------
>
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